My furnace starts up, I have it set for 70 or 72 and it stops producing heat at about 66. I shut it down and attempt to restart it and it gets to the electronic ignition spark but I don't get light off again? It has done this several times, it doesn't produce heat again until it cools off.

You might have a high limit safety switch opening up killing the power going to gas valve,and it doesn`t close back up till it cools down. This is caused by overheating or flames in unit burning outside the burners. This usually caused by a burned out heat exchanger and needs to be replaced,, this can be dangerious,, you need a hvac pro to check it out